Elie Wiesel, the Auschwitz survivor who became an eloquent witness for the six million Jews slaughtered in World War II and who, more than anyone, seared the memory of the Holocaust on the world’s conscience, died on Saturday at his home in Manhattan. He was 87.

Menachem Rosensaft, a longtime friend and the founding chairman of the International Network of Children of Jewish Survivors, confirmed the death in a phone call.

Mr. Wiesel was the author of and was a charismatic lecturer and humanities professor. In 1986, he was awarded the Nobel Peace Prize. But he was defined not so much by the work he did as by the gaping void he filled. In the aftermath of the Germans’ systematic massacre of Jews, no voice had emerged to drive home the enormity of what had happened and how it had changed mankind’s conception of itself and of God. For almost two decades, the traumatized survivors — and American Jews, guilt-ridden that they had not done more to rescue their brethren — seemed frozen in silence.

“He was a singular moral voice,” said Sara J. Bloomfield, the museum’s director. “And he brought a kind of moral and intellectual leadership and eloquence, not only to the memory of the Holocaust, but to the lessons of the Holocaust, that was just incomparable. There is nothing that can replace the survivor voice — that power, that authenticity.”

Yet the plight of Jews was foremost. In 2013, when the United States was in talks with Iran about limiting that country’s nuclear weapons capability, Mr. Wiesel took out a full-page advertisement in The Times urging Mr. Obama to insist on a “total dismantling of Iran’s nuclear infrastructure” and its “repudiation of genocidal intent against Israel.”

A year earlier, on April 19, 1985, Mr. Wiesel stirred deep emotions when, at a White House ceremony at which he accepted the Congressional Gold Medal of Achievement, he tried to dissuade President Ronald Reagan from taking time from a planned trip to West Germany to visit a military cemetery there, in Bitburg, where members of Hitler’s elite Waffen SS were buried.

“He raised his voice, not just against anti-Semitism, but against hatred, bigotry and intolerance in all its forms,” the president said in a statement on Saturday. “He implored each of us, as nations and as human beings, to do the same, to see ourselves in each other and to make real that pledge of ‘never again.’”

Mr. Wiesel long grappled with what he called his “dialectical conflict”: the need to recount what he had seen and the futility of explaining an event that defied reason and imagination. In his Nobel speech, he said that what he had done with his life was to try “to keep memory alive” and “to fight those who would forget.”

Elie Wiesel, the Auschwitz survivor who became an eloquent witness for the six million Jews slaughtered in World War II and who, more than anyone else, seared the memory of the Holocaust on the world’s conscience, died on Saturday at his home in Manhattan. He was 87.

Elie Wiesel, the Auschwitz survivor who became an eloquent witness for the six million Jews slaughtered in World War II and who, more than anyone, seared the memory of the Holocaust on the world’s conscience, died on Saturday at his home in Manhattan. He was 87.

Mr. Wiesel had a leading role in the creation of the United States Holocaust Memorial Museum in Washington, serving as chairman of the commission that united rival survivor groups to raise funds for a permanent structure. The museum became one of Washington’s most powerful attractions.

Mr. Wiesel condemned the massacres in Bosnia in the mid-1990s — “If this is Auschwitz again, we must mobilize the whole world,” he said — and denounced others in Cambodia, Rwanda and the Darfur region of Sudan. He condemned the burnings of black churches in the United States and spoke out on behalf of the blacks of South Africa and the tortured political prisoners of Latin America.

Mr. Wiesel was the author of several dozen books and was a charismatic lecturer and humanities professor. In 1986, he was awarded the Nobel Peace Prize. But he was defined not so much by the work he did as by the gaping void he filled. In the aftermath of the Germans’ systematic massacre of Jews, no voice had emerged to drive home the enormity of what had happened and how it had changed mankind’s conception of itself and of God. For almost two decades, both the traumatized survivors and American Jews, guilt-ridden that they had not done more to rescue their brethren, seemed frozen in silence.

Mr. Reagan, amid much criticism, went ahead and laid a wreath at Bitburg. Paradoxically, the confrontation led to Mr. Wiesel’s to Germany. He said afterward that he had been extremely moved by the young German students he met and the depth of their painful search for an understanding of their country’s past. He urged reconciliation.

“Has Germany ever asked us to forgive?” Mr. Wiesel asked. “To my knowledge, no such plea was ever made. With whom am I to speak about forgiveness, I, who don’t believe in collective guilt? Who am I to believe in collective innocence?”

For much of his life, Mr. Wiesel grappled with what he called his “dialectical conflict”: the need to recount what he had seen and the futility of explaining an event that defied reason and imagination. In his Nobel speech, he said that what he had done with his life was to try “to keep memory alive” and “to fight those who would forget.” “Because if we forget, we are guilty, we are accomplices,” he said.

Central to Mr. Wiesel’s work was reconciling the concept of a benevolent God with the evil of the Holocaust. “Usually we say, ‘God is right,’ or ‘God is just’ — even during the Crusades we said that,” he once observed. “But how can you say that now, with one million children dead?”

In his 1966 book, “The Jews of Silence: A Personal Report on Soviet Jewry,” Mr. Wiesel called attention to Jews who were being persecuted for their religion and yet barred from emigrating. “What torments me most is not the Jews of silence I met in Russia, but the silence of the Jews I live among today,” he said. His efforts helped ease emigration restrictions.

Mr. Wiesel was the author of several dozen books and was a charismatic lecturer and humanities professor. In 1986, he was awarded the Nobel Peace Prize. But he was defined not so much by the work he did as by the gaping void he filled. In the aftermath of the Germans’ systematic massacre of Jews, no voice had emerged to drive home the enormity of what had happened and how it had changed mankind’s conception of itself and of God. For almost two decades, the traumatized survivors — and American Jews, guilt-ridden that they had not done more to rescue their brethren — seemed frozen in silence.

“He raised his voice, not just against anti-Semitism, but against hatred, bigotry and intolerance in all its forms,” the president said Saturday in a statement. “He implored each of us, as nations and as human beings, to do the same, to see ourselves in each other and to make real that pledge of ‘never again.’”